This is one of the [tag]youth baseball practice drills[/tag] we use at the end of practice, usually as a reward for a good practice.   The kids ask for it because it is fun and fast paced; it is a base running/sliding drill.

Start with all your players at home plate. They will go in pairs 1 to 2 seconds apart.

Have a base coach at first. Instruct the lead runner to run through the bag simulating a play at first.
Have the trailing runner round the base like an extra base hit; the runner will slide into 2nd base. Those 2 runners will stay at their respective bases and when you send the next pair the runner at 1st will run first to third sliding into 3rd base, the runner at second goes from second to home simulating scoring on a base hit from 2nd.

This is a fast paced [tag]baseball[/tag] drill that is a lot of fun.   The competitive factor   increases their speed and they don’t realize the conditioning they are getting at the same time!